This invention relates to radio frequency antennas, including various compact high performance active antennas designed to receive a broad spectrum of television, radio, or other like signals.
The field of radio frequency receiving antennas for indoor applications is extensive and well understood within the constraints of traditional antenna designs. Passive antennas require that the receiving element bear some geometric relationship to the wavelength and propagation properties of the signal being received. They therefore need to be adjusted or otherwise modified when changing wavelengths. Similarly, traditional active receiving antennas rely on a good impedance match in order to efficiently couple received power to the receiver. Unfortunately, this requirement also constrains the range of frequencies that can be efficiently received. Furthermore, active antennas and their associated electronics tend to be fairly large and somewhat costly and need to be manually adjusted on a channel-by-channel basis.
This invention is particularly relevant to, among other fields, the emerging field of datacasting in which digital data (which may represent files containing movies, music, software, video games, or other digitally encoded content) is attached to or inserted in a television or radio station's broadcast signal. A receiver in the home or business then tunes in the subject signal and extracts the digital data needed to recreate the content being distributed. These files could be, by way of example, MP-3 music files, or MPEG video files. To be truly suitable for such an application, certain embodiments according to the present invention contemplate a datacasting receiver that should be relatively inexpensive, able to automatically tune to the particular station over which the data is being broadcast, acquire relatively weak television signals with no manual intervention, and remain insensitive to the physical orientation of the receiver. Various embodiments of the invention can be useful in any context where improved radiofrequency wave reception is desired.
Compact and highly sensitive active receiving antennas according to various embodiments of this invention can receive a wide range of broadcast television and other frequencies. Certain embodiments of the invention provide an antenna with a compact form-factor that can be concealed in any one of a number of end user datacasting or other reception devices, both fixed and mobile. Furthermore, various embodiments of the invention can be reasonably omni directional to minimize device orientation issues. They may also be highly sensitive across a wide spectrum of TV signals and can provide effective indoor reception of TV signals at what would normally be the edge of the so-called “B-contour” of the transmitter tower. That contour refers to the geographical area served by a given transmitter in which the received television signal is viewable without excessive noise and static. Previous efforts in the area of traditional indoor TV antenna designs and active receiving antennas have not met these goals in a single solution.
An embodiment of the invention that is disclosed herein incorporates a “cascade” amplifier. Cascade amplifiers have occasionally been used as part of stand-alone radio frequency amplifier applications such as disclosed by Picket (U.S. Pat. No. 4,754,233) or Osawa, et al (U.S. Pat. No. 4,587,495). There has also been some work in the area of cascade amplifiers for improving the transmission of radio frequency signals. For example, Yamamoto et al (U.S. Pat. No. 6,066,993) teaches such a use. All of these references are incorporated herein by this reference. A previous design for a receiving antenna that approaches some of the above-stated goals is Naito (U.S. Pat. No. 5,172,126), which is incorporated herein by this reference. It discloses use of what is effectively a non-resonant e-field probe and suggests an embodiment that could serve as a compact, high gain antenna. However, Naito's design precludes its use for datacasting or other consumer wideband applications since, among other things, it relies on two bipolar transistors in the receiving element. Both such transistors are limited by the reactive impedance of the parasitics, such that each antenna so fabricated would be limited in terms of the wavelength it could receive with any useful gain.
In contrast, in datacasting and certain other broadband applications, the signal of interest may be associated with any one of a wide range of broadcast wavelengths from VHF television to UHF Television or other frequencies used by FM Radio stations. Such signals are thus not of a type where the wave length may be known or ascertained before the fact. Consequently, the end user's receiving device must be manufactured with an antenna capable of effectively receiving a very broad range of wavelengths and be relatively insensitive to physical orientation while having a low manufacturing cost suitable of consumer grade electronics.
To address these heretofore unmet needs, among others, various embodiments of the present invention use a high transconductance transistor as the primary signal amplification element. One such readily available transistor having the required characteristics is commonly known as a “field effect transistor” or “FET.” Field effect transistors have impedances that can be orders of magnitude higher than other transistors, enabling a far greater range of operation. The novel combination of a field effect transistor with a bipolar transistor in a cascode amplifier configuration, as found in some aspects and embodiments of the present invention, provides an antenna design that works in a commercially viable manner. Another preferred embodiment employs a nondissipative feedback loop in which a high efficiency transformer is used in conjunction with one or more high transconductance transistors. This novel architecture has the characteristics of having a high input resistance, low input capacitance, low noise and a very high second and third order Intercept Point. Such a design meets the unique needs for an antenna intended to be built into a datacasting receiver and also offers numerous advantages in other applications as well.